Tuning exciton energy and fine-structure splitting in single InAs quantum dots by applying uniaxial stress

Abstract

Exciton and biexciton emission energies as well as excitonic fine-structure splitting (FSS) in single InAs/GaAs quantum dots (QDs) have been continuously tuned in situ in an optical cryostat using a developed uniaxial stress device. With increasing tensile stress, the red shift of excitonic emission is up to 5 nm; FSS decreases firstly and then increases monotonically, reaching a minimum value of approximately 10 μeV; biexciton binding energy decreases from 460 to 106 μeV. This technique provides a simple and convenient means to tune QD structural symmetry, exciton energy and biexciton binding energy and can be used for generating entangled and indistinguishable photons.

Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies

“…FSS in neutral excitons originates from the atomistic anisotropy in the GaAs zincblende structure, spin–orbit interactions, and the electron–hole exchange interactions . This effect can be detrimental to generating entangled photon pairs from biexciton cascade and several methods have been conducted to minimize the FSS, such as droplet epitaxy, applying uniaxial strain, and magnetic field . Spectral diffusion originates from the change of occupancies of the trap states around a QD.…”

Symmetric Excitons in an (001)-Based InAs/GaAs Quantum Dot Near Si Dopant for Photon-Pair Entanglement

“…Cascade emission in a semiconductor quantum dot (QD) from the biexciton state XX to the ground state G via the intermediate exciton states X (|↑⇓⟩ and |↓⇑⟩, ↑, ↓: electron, ⇑ , ⇓: hole spin) can emit polarization-entangled photon pairs |LR> +|RL> (R (L): right (left) circular polarization). However, a real epitaxial QD with in-plane anisotropy (e.g., [1][2][3][4][5][6][7][8][9][10] and [110] on (001) plane) shows X1 and X2 (|↑⇓⟩ ± |↓⇑⟩) with fine structure splitting (FSS) and horizontal (H) or vertical (V) linearly polarized two photon emission in a state |HH> + e iT 1 FSS/ħ |VV> (T1: time delay between XX and X photons, i.e., intrinsic X radiative lifetime Tx, Figure 1a). The FSS must be smaller than a lifetime-limited radiative linewidth 1/(2πT1) (e.g., 4.9 μeV for T1 = 134 ps fasten in a microcavity [1]) to erase decay-path information for entanglement [2][3][4].…”

“…The FSS must be smaller than a lifetime-limited radiative linewidth 1/(2πT1) (e.g., 4.9 μeV for T1 = 134 ps fasten in a microcavity [1]) to erase decay-path information for entanglement [2][3][4]. For strain-driven (001)-based InAs QDs with a flexible wavelength (λ), 870~1600 nm [5][6][7][8], structures (e.g., strain-coupled QD bilayer [5], dot-in-barrier [6], or dot-in-well [7]) and microcavity integration, it shows FSS > 10 μeV [9][10][11][12] typically and spin scattering time Tss ~1.9 ns [2]. The FSS can be reduced by growing C3v QD on (111) surface [13][14][15][16][17] or a post-grown electric field (different Stark shifts for X1 and X2) [18,19] or stress [10,11,20,21] tuning.…”

“…For strain-driven (001)-based InAs QDs with a flexible wavelength (λ), 870~1600 nm [5][6][7][8], structures (e.g., strain-coupled QD bilayer [5], dot-in-barrier [6], or dot-in-well [7]) and microcavity integration, it shows FSS > 10 μeV [9][10][11][12] typically and spin scattering time Tss ~1.9 ns [2]. The FSS can be reduced by growing C3v QD on (111) surface [13][14][15][16][17] or a post-grown electric field (different Stark shifts for X1 and X2) [18,19] or stress [10,11,20,21] tuning. Due to a deviation of X1 and X2 from the main crystal axis [110] and [1][2][3][4][5][6][7][8][9][10], the erasure of FSS requires a biaxial stress (in-plane) tuning or a combination of stress (in-plane) and electric field (vertical) tuning.…”

“…The FSS can be reduced by growing C3v QD on (111) surface [13][14][15][16][17] or a post-grown electric field (different Stark shifts for X1 and X2) [18,19] or stress [10,11,20,21] tuning. Due to a deviation of X1 and X2 from the main crystal axis [110] and [1][2][3][4][5][6][7][8][9][10], the erasure of FSS requires a biaxial stress (in-plane) tuning or a combination of stress (in-plane) and electric field (vertical) tuning. Besides, QD geometrical anisotropy (e.g., shape, strain or charged environment) induces light hole (lh)-heavy hole (hh) mixing (in degree β) and photon polarization mixing as the emission intensity polarization (EIP) reflects [22][23][24], which is quite correlated to the growth parameters such as growth temperature, indium deposition amount and surface migration time.…”